您的问题是， undefined属性：您正在将左更改为 239px ，但不要显式指定为 0 。因此，它默认为 auto ，该值没有到 239px 的有效平滑过渡。

Your problem is that you are trying to animate from an undefined property: you are changing left to 239px, but don't explicitly specify it as 0 initially. It therefore defaults to auto, a value for which there is no valid smooth transition to 239px.

向基本定义中添加 left：0 即可。

Add left:0 to the base definition and you will be fine.

请参阅这里的JSfiddle演示您在Chrome 32+中的问题。